The present invention relates to a method of executing a hemming process for folding a hem flange of an outer panel and combining an inner panel therewith and an apparatus for implementing this method in the course of manufacturing an external plate body like a hood, fenders, side-doors, and a luggage room, of an automotive body, for example.
For instance, when processing an external plate body such as a hood, fenders, side-doors, or the like, available for assembling an automotive body, a hem flange formed at an edge of an outer panel is folded in the backward direction to cause the folded hem flange to nip an edge of an inner panel in order to combine both panels with each other. Conventionally, this method is called the "hemming process". Concretely, as shown in FIG. 7, a hem flange 11a is previously formed at an edge of an outer panel 11 by erecting it at a substantially right angle. Next, an edge of an inner panel 12 is superposed on the inner surface of the hem flange 11a, and then a preliminary folding process is executed against the superposed hem flange 11a by a predetermined folding angle by operating a preliminary-folding blade 13. Finally, the hem flange 11a is regularly folded by means of a regular folding blade 15.
However, when executing a hemming process, generally, how to process corner domain of the hem flange 11a is an important problem. This is because, in the course of folding corner domain of the hem flange 11a backward in the direction of an edge of an inner panel, a certain excessive substance is naturally generated to inevitably result in the generation of numerous creases. Once numerous creases are generated, it not only spoils external appearance, but it also causes part of the creases to protrude from the contour of the corner domain to eventually generate a security problem. Furthermore, deformation may be generated on the external surface of an outer panel.
To prevent those critical problems from occurrence, as shown in FIG. 8, conventionally, the dimension of corner domain 11a1 is reduced so that depth S3 of the hem flange 11a can extremely be contracted from the other depth S4 of peripheral domains other than the corner domain 11a1, thus decreasing the amount of excessive substance of the corner domain 11a1.
Furthermore, as shown in FIG. 9, any of those conventional folding methods terminates the preliminary folding process without further executing a regular folding process against the corner domain 11a1.
Nevertheless, according to such a conventional method cited above, although a crease can be prevented from occurrence in the corner domain, since this conventional method deletes the regular folding process, special treatment is discretely needed in order to fill up clearance between the corner domain 11a1 and the inner panel 2 with a sealing agent or paint, thus increasing an additional step. Desirably, such an additional step should be eliminated.